A polyoxymethylene resin has been generally known to have an excellent mechanical property, creep resistance, fatigue resistance, and friction and wear resistance as engineered plastics, and thus may be applied to various industries and industrial products, such as electrical/electronics instrument or vehicles. However, the currently used polyoxymethylene resin may have drawbacks. For example, thermal stability of conventional polyoxymethylene resin may be poor and decomposition may occur due to thermal impact, mechanical impact, or additives during a forming process. Particularly, when a colorant is used, decomposition may significantly progress, brittleness may increase, and processability may be reduced.
Therefore, there has been a growing demand for improvement of such polyoxymethylene resin, particularly for vehicle parts, in which heat resistance, a lubricating property, and the like, may be required and various kinds of mechanical properties and forming properties may be required due to frequent operations, operation friction, and the like. For example, among the vehicle parts, a door checker may be a part to which a polyoxymethylene resin formed material is generally applied. Since, the door checker allows a door of a vehicle to be opened in stages when the door of the vehicle is opened, improved heat resistance, the lubricating property, the forming property, and various mechanical properties may be required.
Various methods in related arts have been developed to improve thermal stability of polyoxymethylene. A polyoxymethylene resin composition including (A) 100 parts by weight of a polyoxymethylene polymer that is a homopolymer or a copolymer of oxymethylene and has a molecular weight of 10,000 to 200,000 g/mol; (B) 0.01 to 5 parts by weight of a melamine resin; and (C) 0.01 to 5 parts by weight of a polyoxyethylenepolyoxypropylene block copolymer that has an average molecular weight of 7,000 or more and less than 10,000 has been reported to improve thermal stability. In another example, a polyoxymethylene resin composition which includes (B) 0.005 to 2 parts by weight of an amine-substituted triazine compound, (C) 0.01 to 5 parts by weight of a compound where 0.05 to 5 wt % of maleic anhydride is grafted to an ethylene-propylene copolymer and an ethylene-propylene trimer, and (D) 0.001 to 2 parts by weight of 1,12-dodecane dicarboxylic acid dihydrazide based on (A) 100 parts by weight of a polyoxymethylene polymer has been developed. Meanwhile, although the examples of the related arts may reduce generation of formaldehyde gas and improve thermal stability, a tribology property and hardness thereof may not be improved.
In this respect, a polyacetal composition including (i) a polyacetal resin, (ii) a p-aramide particle, and (iii) a vinyl-ended dimethyl siloxane polymer, has been provided and the composition may have an improved tribology property. However, since viscosity of the vinyl-ended dimethyl siloxane polymer used in the composition is substantially high, uniform mixing may not be performed during compounding. Therefore, long-term dimensional stability of a formed article may be reduced, a forming property may be insufficient, and compatibility with polyoxymethylene may be reduced, thereby causing an exfoliation phenomenon during injection and extrusion forming. Further, when the composition is formed, siloxane may be exposed on a surface of the formed article. As result, when the composition is applied to a formed material, the composition may be prohibited from use in silicone free products.
In addition, various polyoxymethylene resin compositions including polyoxymethylene, a thermoplastic resin, an aramide fiber, urea, and the like, have been developed. However, these resin compositions may be slightly different in their constituents, and insignificant improvement in physical properties, such as heat resistance, dimensional stability, a forming property. Therefore, there is still an unmet need in the technical field for developing a novel resin.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.